Photographic color-positive transparency films, such as 35 mm (Type 135) slides and larger-format sheet films, are commonly used to capture and reproduce original images. Color-positive transparency films are well suited for these applications because they are capable of extraordinary image quality, producing images exhibiting high sharpness, low noise, extensive luminance dynamic range, and large color gamut. Color-positive transparency films are designed so that the images they produce will have an appropriate appearance when illuminated and viewed by projection in a darkened room, or by back-illumination.
Color-image reproduction systems known in the art permit images to be captured by color-transparency film media as well as by other dissimilar image-receptive media or devices, possibly digitized and stored, and then output onto complementary media. So, for instance, color images may be captured on color-positive photographic media, and then illuminated and viewed directly by projection in a darkened room or by back-illumination, or copied onto larger or smaller transparencies, or printed onto positive photographic paper. Such images may or may not pass through a digital intermediary. In another case, color images may be first captured on negative film and then reproduced on negative photographic paper. Again, such images may or may not pass through a digital intermediary. In yet another case, color images may be captured as an electronic signal by a digital-still or video camera, and then viewed on an electronic display or converted to print by a device such as a thermal printer. Again, such images may or may not pass through a digital intermediary. The foregoing are just some examples of color-image reproduction systems.
Color-imaging systems in which the image passes through a digital intermediary allow improvements to be made to an image using a single means, which may be a digital computer. Thus, improvements to an image's color and tone scale, as well as to its sharpness and noise, can be made in a convenient and adaptable way. Furthermore, if the imaging system includes a means for rapid viewing of the changes, the content of an image can also be edited in a convenient fashion. Many of these types of improvements are known to those skilled in the art. For example, U.S. Pat. No. 4,500,919 entitled “COLOR REPRODUCTION SYSTEM” by W. F. Schreiber, discloses an image-reproduction system of one type in which an electronic reader scans an original color image and converts it to an electronic image. A computer workstation and an interactive operator interface, including a video monitor, permit an operator to edit an image by means of displaying it on the monitor. When the operator has composed a desired image on the monitor, the workstation causes the output-writer device to make an inked output of the reproduced image.
U.S. Pat. No. 5,956,044 entitled “IMAGING DEVICE TO MEDIA COMPATIBILITY AND COLOR APPEARANCE MATCHING WITH FLARE, LUMINANCE, AND WHITE POINT COMPARISON” by E. J. Giorgianni and T. E. Madden describes a system for producing intermediary image-bearing signals and/or encoded data compatible for subsequent imaging applications from disparate and inherently incompatible types of input imaging devices and media, including color-positive transparency media. The invention gives consideration to the input and output-image viewing environments in terms of their viewing-illuminant spectral energy distribution, amount of viewing flare light, surround type, and observer adaptive white point chromaticities. Application of the methods and means of that invention produces intermediary image-bearing signals and/or data that can be output onto any of a plurality of image-receptive media and/or image-forming devices such that any output image should match the appearance of any input image based on the capabilities and limitations of the specific output device and/or medium and on the specific application for which the image is being produced. Digital color-signal processing transforms are applied to input image data based on differences in the viewing conditions for the input image and a set of defined reference viewing environment.
Many color-positive transparency film images have cyan-blue balanced reproduced neutrals, which appear achromatic to a human observer when viewing the projected film image in a darkened room. That is because an observer's visual system tends to adapt to the projected image itself due to the lack of visual cues in the darkened viewing environment. In a typical darkened film-projection viewing environment however, that adaptation is not complete due to the highly reddish-yellow projector lamp chromaticity, the fairly low absolute luminance level of the projected image, and the fact that the projected images fills only a portion of the observer's field of view. The overall measured cyan-blue color balance of the color-positive transparency film image, combined with the observer's partial or incomplete chromatic adaptation to the described projection conditions, results then in images that appear to be properly color balanced. The effect of the observer's partial or incomplete chromatic adaptation is addressed in U.S. Pat. No. 5,956,044 through the use of a chromatic adaptation transform, such as a VonKries transformation matrix, or by using any of a number of other techniques known to those skilled in the art.
The overall cyan-blue color balance of most color-positive photographic transparency film media results from the intentional design and manufacturing of film. FIG. 1 shows the cyan, magenta, and yellow density scales for a typical photographic color-transparency film. The unequal CMY density values of the reproduced grayscale shown produce the desirable cyan-blue color balance described earlier, i.e. at a given scene luminance-factor value, there is a greater amount of cyan and a lesser amount of yellow density produced. The overall cyan-blue color balance resulting from these unequal density values is considered in the above cited-references, but only in relation to white-balancing and observer chromatic adaptation.
Application of a sequence of transforms to modify images is taught by U.S. Pat. Nos. 5,452,111; 5,420,979; and 5,786,823.
It would thus be desirable to provide methods and systems for encoding image data derived from photographic color-transparency films such that images reproduced from the image data derived from such media appear appropriately rendered without requiring references to their origin.